Conventional antilock braking systems (ABS) and drive slip regulating systems (ASR) are designed to regulate on the basis of a fixed coefficient of friction between the wheel and the road surface, usually the coefficient of friction for a dry road with good gripping properties. Corresponding to the coefficient of friction is a (critical) wheel load-dependent driving torque which can still be transmitted to the road surface without exceeding a permissible slip limit, i.e. without spinning of the driving wheel. A change in the coefficient of friction, e.g. due to wet or icy road surfaces, can lead to an impairment of the regulating characteristics. In antilock braking systems, for example, such a change in coefficient of friction can result in a lengthening of the braking distance on slick icy roads. Therefore, it is desirable to adapt the regulating characteristics of such systems to the state of the road being traveled at the time.
In a regulating system for antilock braking systems and drive slip regulating systems known from DE 38 14 956 A1, the current coefficient of friction and the slope of the slip curve are calculated from the transmitted driving torque or braking torque and the rotating speed of a driving wheel. Thus, there is no exact determination of the coefficient of friction.